Antenna fabrication method

ABSTRACT

A PLURALITY OF ANTENNA HORNS ARE ARRANGED IN AN ASSEMBLY TOOL, AN ADHESIVE FILM IS APPLIED BETWEEN THE HORNS AND THE ENTIRE ASSEMBLY IS PLACED IN AN OVEN TO CURE.

Allg. l, 1972 w. D, w|| |AMs EI'AL 3,681,162

ANTENNA FABRICATION METHOD Filed DBC. 27, 1968 BYN ol 0 O ,n o o o o o o 'o o FIG. I

WorenvDW-illioms Loring B. Andrews Frank Baden.

United States Patent O ABSTRACT OF THE DISCLOSURE A plurality of antenna horns are arranged in an assembly tool, an adhesive film is applied between the horns and the entire assembly is placed in an oven to cure.

4 Claims BACKGROUND OF TI-[E INVENTION The physical accuracy with which the horn antennas of a horn array antenna must be placed is directly related to the electrical tolerances imposed on the horn antenna array. The over-al1 error of a horn antenna array is related to the tolerances of the horn antennas of the array and the exactness of their location within the array. The antenna designer is reluctant to allow for mechanical error, and, therefore, proper antenna performance demands minimum physical tolerances.

There are several known methods of horn antenna array fabrication. Some require that the horns of the array be brazed, spot welded, or banded together. Since the horns must be fabricated to meet close tolerances, expensive tooling and assembly problems are encountered.

SUMMARY OF TH=E INVENTION In the present invention, strips of expandable adhesive are tacked to the sides of each antenna horn element. The prepared elements are then placed in the curing xture in a staggered pattern and the loaded fixture is placed in an oven to cure. The assembly tool allows for exact placement of each horn antenna and thus prevents the physical tolerances of the horns from being cumulative in the array. The adhesive is capable of bonding the horns together as long as the gap between the horns is between a minimum and maximum bonding distance commensurate with the particular adhesive being used.

BRIEF DESCRIPTION OF DRAWING This invention will become more easily understood and readily apparent from the following detailed description of this invention, of which the accompanying drawing forms an integral part.

In the drawing:

FIG. 1 is a plan view partially cut away of an antenna array according to this invention; and

FIG. 2 is a side view of an antenna horn with a portion thereof cut away and showing mounting of the horn relative to an assembly tool.

DESCRIPTION OF TI-IE PREFERRED EMBODIMENT The horns 3 of the horn antenna array 1 are placed in an assembly tool 5 and then joined together. The assembly tool consists of machined locating blocks 7, one for each horn, which are permanently attached to a base support plate. Exact placement of the locating blocks on the base plate 9 enables the horn antennas to be accurately arranged in the array. The size of the locating blocks is established by the minimum internal dimension of the die cast horn antenna. The horns are pressed down until they seat against the base plate, and thus, the base plate 3,681,162 Patented Aug. I, 1972 ICC provides accurate planar alignment of the array aperture while the locating blocks provide accurate inter-element positioning of the horn antennas in the array. To provide vertical constraint, the slot or opening in the rear of the die cast horn may be used to accept a threaded rod 11 or similar hold down clamp. The center-to-center distances of the horn antennas is a function of the aperture tolerance and the horn lit on the locating blocks. Thus, the accuracies of module fabrication are built into the assembly tool. Tolerances are not accumulative in the assembly technique as they would be if each horn was welded directly to other horns to form the array. Instead, they are automatically averaged out across the array. This method of assembly results in a more uniform module and permits exacting control in the assembly of the modules into an over-all array.

The die cast horns are cleaned in any conventional caustic dip and coated with dichromate. The assembly fixture is prepared by Waxing it with a paste wax such as Johnsons wax and then spraying it with a commercially available separating film. This treatment facilitates removal of the cured module from the fixture and, in the event of adhesive squeeze-out, will prevent anything from adhering to the fixture.

The adhesive lilm 13, a vinyl phenolic adhesive system of a predetermined thickness commensurate with the tolerance of the horns, is positioned about the sides of the horns. The adhesive ilm is tacked to the horns using a 50-50 mixture of vinyl phenolic and a solvent blend. The horn is then placed on the assembly fixture and locked into place. The entire assembly is then placed in an oven to cure.

The critical factor in the cure cycle is the warm up time of the module. The adhesive film has a volatile solvent content which can be adjusted by the manufacturer up to as high as 35 percent. The volatile portion is usually l5 to 3'5 percent depending on adhesive application. The greater the foaming action or film expansion desired, the larger the volatile content. The critical aspect of film cure is that the softening point temperature of the resins be reached before too much volatile content is evaporated. It is important that the unit being bonded be brought up to the cure temperature (at least 275 F., preferably 325-350 F.) in about thirty minutes. This, of course, has a direct bearing on the type of oven and its heating capacity as well as the mass which is being heated. Aluminum tooling helps in uniform heat transfer to the individual horns, as they do not contact each other. The actual horn temperature is monitored with copper-constantine thermocouples. It is obvious, then, that the long dwell time at temperature below the softening point of the resins will only drive olf the volatile solvents and markedly reduce the total expansion of the adhesive film.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specilically described.

We claim:

1. A method of fabricating a horn antenna array comprising the steps of: applying expandable adhesive bonding film composed of a vinyl phenolic adhesive system about the sides of a plurality of antenna horns; positioning and securing said antenna horns on an assembly tool in the form of an array; and curing the resulting assembly at S25-350 F. to bond said horns into an integral unit.

2. A method of fabricating a horn antenna as set forth in claim 1 wherein said antenna horns are dipped in a caustic dip and then coated with a dichromate coating before being positioned on said tool.

3. A method of fabricating a horn antenna as set forth in claim 2 wherein said assembly tool is waxed and then sprayed with a separating lm before the horns are placed thereon.

4. A method of fabricating a horn antenna as set forth in claim 3 wherein the horns are positioned with predetermined gaps and said gaps are filled with said expandable adhesive bonding ilrn upon curing.

References Cited UNITED STATES PATENTS OTHER REFERENCES The Condensed Chemical Dictionary, Fifth edition, Reinhold Publishing Corporation, New York, 1956, p.

CARL D. QUARFORTH, Primary Examiner EE. E. LEHMANN, Assistant Examiner U.S. C1. X.R. 

